Desalting is one of the first steps in crude refining. This is done to remove salts and particulates to reduce corrosion, fouling and catalyst poisoning. In a typical desalting process, fresh water is mixed with oil to produce a water-in-oil emulsion which in turn extracts salt and brine and some particulates from oil. The salty emulsion is then sent to a desalter unit where the application of an electric field forces water droplets to coalesce. Large electrocoalesced water droplets settle under gravity and separate from the desalted oil. Electrocoalescence (i.e. coalescence under electric field) is also used to dehydrate crude at or near production sites to remove water before sending to the refinery.
To aid the desalting process, chemical additives known as demulsifiers are added to crudes and/or emulsions. The material properties of these demulsifiers allow them to remain in the oil phase of an emulsion. These additives reduce the emulsion stability, causing an enhancement in water separation, desalting and electrocoalescence and thus emulsion resolutions.